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Invalid listing during input

I'm doing basic homework that looks like this:

    While input <> -1
        input = CDbl(InputBox("Enter numbers to add, enter -1 to stop"))
        values = values + input
    End While

It works fine until I click "cancel" on the input field. Then I input the string "" and I get the following error:

System.InvalidCastException {"Conversion from string "" 
                              to type 'Double' is not valid."}

I think I understand the error, I am trying to convert using CDbl to a non-numeric value. My question is, what would be the more correct way to write this code? Is this code or just a lack of error handling?

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3 answers


Try using Double.TryParse

Dim value as Double = Nothing
If Double.TryParse(InputBox("Enter numbers..."), value) Then
    values = values + value
End If


My syntax might be off a bit, but you should get the idea

+2


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You can try using Double.TryParse or using a try catch block with Double.Parse. Since this is homework, I'll let you look at them on MSDN.



+4


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You will also get an error if they enter anything other than a double, or a value that is too large to be stored in a double.

The suggestions above should be sufficient, although you essentially want to validate user input before trying to use it.

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